The long term objectives are to understand the degradation and repair processes that occur after acute joint trauma. A canine model system of acute transarticular load will be used to generate tissue for an In vitro investigation on the role that matrix damage plays chondrocyte mediated matrix degradation in the early phase of degeneration. The mechanisms, whereby matrix damage plays a role in the response, will be investigated using a combination of quantitative biochemistry, histology, immunohistochemistry, and in situ hybridization. A biomechanical model of the initial damage will be developed. The in vivo response to the acute damage to the weight bearing area of the medial femoral condyle will be followed. After the temporal sequence is established, the model will be perturbed by anterior cruciate ligament transection. The role of altered forces and motions on acutely damaged cartilage will then be determined. Information from this study will lead to a better understanding the role acute joint trauma plays in the subsequent development of osteoarthritis. Detailed knowledge of the early events in the degradative phase that often occur after the initial trauma, could lead to the rational planning of Intervention for post-traumatic osteoarthritis as well as a better understanding of the osteoarthritic process.